What happens during the denaturation step of PCR?

During the denaturation step of PCR, DNA strands are separated. This step typically involves heating the reaction mixture to around 94 to 98 degrees Celsius. The high temperature breaks the hydrogen bonds between the base pairs in the double-stranded DNA, resulting in two single strands. This separation is crucial because it allows the primers to access the individual single-stranded DNA templates in the subsequent steps of the PCR process.

The other options pertain to different steps in the PCR cycle. For example, the attachment of primers to target sequences occurs during the annealing phase, which involves lowering the temperature to allow the primers to bind to the complementary sequences on the single-stranded DNA. New DNA strands are synthesized in the extension step, where a DNA polymerase enzyme synthesizes new strands by adding nucleotides to the primers. Lowering the temperature for annealing is a distinct process that takes place after denaturation, emphasizing the critical role of the high temperature used exclusively during denaturation.